*3.2.1. Galapagos sea lions*

86 New Approaches to the Study of Marine Mammals

of significance of *p*< 0.05 (α = 0.05).

**3. Results and discussion** 

**3.1. Stable isotope profiles and trophic levels** 

thread herrings and mullets were -17.0 ±0.70 and -9.34 ±0.80.

USA).

signals) [48].

followed the same statistical methods. Statistical comparison tests were conducted at a level

Principal Components Analyses (PCAs) were conducted on the fractions of PCBs and organochlorine pesticides relative to total concentrations by contaminant group (i.e., contaminants expressed as a fraction of total) for each sample to visualize spatial differences in patterns in sea lion pups from different sites within the Galapagos Archipelago and elucidate potential sources (i.e., local versus global-atmospheric). First, samples with undetectable values were replaced by a random number between the lowest and the highest concentration that were detectable (> MDL) to account for uncertainty before PCA (i.e., *trans*-chlordane and PCB 110 showed zero values in blanks in three and two samples out of 20, respectively; therefore; there was not possible to calculate MDLs), or otherwise removed from the PCAs. Secondly, samples were normalized to the concentration total before PCA to remove artefacts related to concentrations differences between samples. Finally, the centered log ratio transformation (division by the geometric mean of the concentration-normalized sample followed by log transformation) was then applied to this compositional data set to produce a data set that was unaffected by negative bias or closure [47]. Regressions, statistical comparisons and PCAs were run using JMP 7.0 (SAS Institute Inc.; Cary, NC,

The values of *δ*15*N* and *δ*13*C* (mean ± standard deviation) found here are consistent to those reported in Galapagos sea lion pups (i.e., 13.1‰ ± 0.5‰ for *δ*15*N*, and -14.5‰ ± 0.5‰ for *δ*13*C*) in a recent study [31].No significant relationship was observed between isotopic values and length of the pups (*δ*15*N*: *r* = 0.005, *p* =0.7594; *δ*13*C:r* = 0.18, *p =* 0.0626) or weight (*δ*15*N:r* = 0.0001, *p* =0.9645; *δ*13*C*: *r* = 0.18, *p =* 0.0752). Although female pups appeared to exhibit higher values of *δ*15*N* compared to male pups (*t*-test = 2.3767, *p* = 0.0288), *δ*13*C* values between males and females were similar (*t*-test = -0.3326, *p* = 0.7433). In addition, no significant inter-site differences in *δ*15*N* (ANOVA, *p* = 0.4235) and *δ*13*C* (ANOVA, *p* = 0.8378) values were found among rookeries. This indicates that site or foraging location had minimal influence on the isotope ratios. The lack of differences was further minimized by sampling similar ontogenetic stages (i.e., pups of similar age, development and size), and a metabolically inactive tissue (i.e., fur hair), which is corroborated by the fact that hair is an inert tissue containing physiological and dietary information (isotopic

Based on the *δ*15*N*values, the trophic level (TL) measured here for the Galapagos sea lion (*δ*15*N* = 13.0; TL = 4.2) fall within the range of those recently reported (i.e., *δ*15*N* =12.6−13.4; TL = 4.1−4.4) elsewhere [30, 31, 43]. The *δ*15*N* values for thread herrings and mullets were 9.4‰ ± 1.77‰ (TL = 3.1), and 12.7‰ ± 1.10‰ (TL = 4.1), respectively, while the *δ*13*C* values for Observed concentrations of selected POPs in Galapagos sea lion and two of its main prey items are summarized in Table 1. Galapagos sea lions represented the largest number of organisms sampled in this study (*n* = 41) and exhibited the highest concentrations of PCBs and OC pesticides. The multi-comparison post hoc analysis, including sea lions and prey fish, showed that no significant differences in OC pesticides and PCB congener concentrations were observed between male and female pups. Fish prey commonly exhibited significantly lower concentrations than Galapagos sea lion pups (ANOVA and multi-comparisons Tukey-Kramer (HSD) post-hoc test, *p*< 0.05) (Table 1, Figure 2).

Concentrations of ∑DDTs in Galapagos sea lions ranged from 16.0 to 1700 *μ*g/kg lipid and ∑DDTs were the predominant OC pesticide in Galapagos sea lion pups, as previously reported [35]. ∑Chlordanes were the second most abundant group of contaminants present. *Trans*-nonachlor represented 68% of ∑chlordanes, followed by *cis*-chlordane, *cis*nonachlor and *trans*-chlordane (Table 1), a pattern comparable to that reported in pups of southern elephant seals (*Mirounga leonina*) [49] and Weddell seals (*Leptonychotes weddellii*) [50]. This indicates that *trans*-nonachlor is a predominant chlordane compound in pinnipeds.

Within the hexachlorocyclohexanes (HCHs), *β*-HCH was the only isomer detectable in all pups (>MDL). *β*-HCH was the dominant HCH isomer in blubber samples of California sea lions (*Zalophus californianus*) from Baja California [51] and in toothed cetaceans from tropical and temperate waters of the Indian and North Pacific oceans [52] due to the greater biomagnification of the most bioaccumulative *β*-HCH versus *γ*-HCH [3, 20]. Interestingly, the mean *β*-HCH concentration in Galapagos sea lions was higher than the mean ∑HCH concentrations measured in spinner dolphins (*Stenella longirostris*) (21.3 *μ*g/kg lipid) captured in a marine area of the Eastern Tropical Pacific [52] in offshore waters north of the Galapagos.

Both dieldrin and mirex were detected in all pups with concentrations ranging from 0.85 to 24 *μ*g/kg lipid for mirex and from 9.00 to 83.0 *μ*g/kg lipid for dieldrin. Concentrations of ∑PCBs (i.e., sum of 20 PCB congeners) ranged between 16.0 and 380 (*μ*g/kg lipid) in pups and from 1.0 to 140 (*μ*g/kg lipid) in fish preys (Table 1).
